3D Printing in Metal! Surely that is not possible?

3D printing can create functional metal parts printed directly from CAD. [snip] The ProMetal three dimensional printing process is an accurate, flexible, and reliable tool that can create extremely intricate metal tools, workpieces and molds. In many cases, ProMetal is capable of producing components that would be impossible to produce by any other means. ExOne holds patents on 3D Printing in Metal [snip] As I write this, I'm making things mostly by direct-metal printing: there's a machine that takes a CAD file specifying a 3D object, and builds the object, physically, as metal. If this sounds like science fiction to you, well it might. I don't (yet) have this machine on my desk, I just rent time on it. The process that I use is proprietary to Ex One, and they do the printing. What follows is very much a layman's explanation of how it works -- for more technical information, please visit Ex One's Prometal site. (Some information about other types of 3D printing is here.) To start with, the design is laid down, one layer at a time, in stainless-steel powder held in place by a laser-activated binder. You can see the layering on the finished pieces, it is the source of the characteristic texture of my work. Each layer is .004" to .007" thick. The steel granules are so fine that they feel like very heavy, cool flour. During the build the extra unbound powder supports the piece, so no extra structure is needed to handle undercuts. The powder is very flowable, it's not caky like cornstarch, so removing this extra supporting powder from the finished model is quite easy. It slides off with a little shake and a light brush, and it can be poured out of interior spaces. After the whole model is built up, and the extra powder is shaken off, the piece goes into an oven, where heat drives off the binder and fuses the steel powder. There's just enough heat to make the granules weld together where they touch, without collapsing the entire piece into a puddle. This produces a porous steel part that's about 60% dense, like the one at left. This "green" material is matte gray, feels like sandstone, and won't take a polish. It is soft enough to cut quickly with a hacksaw, but can't quite be dented with a fingernail. It's considerably lighter than steel, which is not surprising since it's 40% air. An artist exploring math and science in sculpture using 3D Printing in a variety of media